Revert "Delete MTLLoader.js"

This reverts commit d607e919fda4bf1a0f2e0e0574435cc367f21b66.
Revert "Delete OBJLoader.js"

This reverts commit b3619221754509db78403bfdf6ee28584d25ce37.
Revert "Delete OBJMTLLoader.js"

This reverts commit 326a6ac2cc08024647eaf180fba81f99db82a08a.